[gsb] show a fixit if the subject type is a member type

Author: Suyash Srijan

lib/AST/GenericSignatureBuilder.cpp

@@ -5755,7 +5755,7 @@ GenericSignatureBuilder::finalize(SourceLoc loc,
 
   // Emit a diagnostic if we recorded any constraints where the constraint
   // type was not constrained to a protocol or class. Provide a fix-it if
-  // allowConcreteGenericParams is true.
+  // allowConcreteGenericParams is true or the subject type is a member type.
   if (!invalidConstraints.empty()) {
     for (auto constraint : invalidConstraints) {
       auto loc = constraint.sourceLoc;
@@ -5775,7 +5775,7 @@ GenericSignatureBuilder::finalize(SourceLoc loc,
         return subjectTypeName;
       };
 
-      if (allowConcreteGenericParams) {
+      if (allowConcreteGenericParams || subjectType->is<DependentMemberType>()) {
         auto subjectTypeName = subjectType.getString();
         auto subjectTypeNameWithoutSelf = getNameWithoutSelf(subjectTypeName);
         Diags.diagnose(loc,

test/Constraints/generics.swift

@@ -662,3 +662,6 @@ protocol SR_7984_HasAssoc {
 struct SR_7984_X<T: SR_7984_HasAssoc> {}
 extension SR_7984_X where T.Assoc.Foo: String {} // expected-error {{type 'T.Assoc.Foo' constrained to non-protocol, non-class type 'String'}} // expected-note {{use 'T.Assoc.Foo == String' to require 'T.Assoc.Foo' to be 'String'}} {{38-39= ==}}
 
+struct S<T: Sequence> where T.Element: String {} // expected-error {{type 'T.Element' constrained to non-protocol, non-class type 'String'}} expected-note {{use 'T.Element == String' to require 'T.Element' to be 'String'}} {{38-39= ==}}
+func F<T: Sequence>(foo: T) where T.Element: String {} // expected-error {{type 'T.Element' constrained to non-protocol, non-class type 'String'}} expected-note {{use 'T.Element == String' to require 'T.Element' to be 'String'}} {{44-45= ==}}
+